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Wicked Wrench
Wicked Wrench, ASE/GM Master Certified 25Years
Category: Cadillac
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Experience:  8 time Cadillac Gold Level Excellence Award Winner
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I have a 1987 Cadillac Deville 4.1 L Engine. The engine hesitates

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I have a 1987 Cadillac Deville 4.1 L Engine. The engine hesitates and bucks when I go uphill. Going uphill the car slows to about 19 mph. It does not matter if the engine is hot or cold. I've change the catalytic converter and the muffler, fuel pressure regulator, and the fuel filter and tested the MAP which P.0.2 is at 102.    The car revs ok on idle but it hesitates when I stomp on the accelerator. If I ease the accelerator down, it does not hesitate. Any solution?
The only thing i can think of is to check the main engine ground at the back of the starter.There is a bulletin to relocate the ground strap from the engine mount bracket to the engine block at the rear of the starter motor.This ground has caused me so many varied problems that it is the first thing i check.
Customer: replied 7 years ago.
I tried that and in addition I changed the O2 sensor and it still does the same thing.
that is a strange one,i will opt out so another expert can answer
Needs a camshaft. Typical 4.1L. If you rev it it pops like backfiring through the T/Body. Needs a stick my friend.

Good Luck!
Customer: replied 7 years ago.
the reving is ok. I can rev it up to 2000 but it is in the accleration going up the hill. Going downhill is ok.
Does it pop, hesitate, skip or backfire going up hills?
Is the secondary ignition system within spec?
Can you put a vacuum gage on it & rev it up without any needle bounce??

Please answer these questions so I can be of further assistance.

Customer: replied 7 years ago.
I drove the car going uphill and it popped abd hesitated tehn it died. I had the car towed home and checked the fuel and it is getting to the TBI but won't start. Did not check the secondary ignition system. What is involved in it?
Bulletin No.: T-88-125
File in Group: 6E
Number: 60 Corp. Ref. No.: 816516
Date: April '88

During a recent analysis of inoperative ignition modules, a dealer submitted an alternate test procedure for diagnosing HEI ignition modules. The test described below requires the use of only three jumper leads and a 12V electrical test light. It is presented here for use when an approved module tester, such as the Kent-Moore tester J-24642-F, is damaged or otherwise unavailable. Use of an approved module tester is still recommended as the primary diagnostic tool for ignition modules. Refer to Section 6E-C4, "Electronic Spark Timing (EST) System" and Section 6D4, "Ignition System" of the appropriate model year Service Information Manual for additional information.


1. Open the 4-way connector at the distributor wire harness.
2. Using two jumper leads reconnect the distributor reference line, circuit 430 (purple/white) and the distributor ground, circuit 453 (black/red).
3. Start the engine. A code "23" will set because the engine is running on Base Timing. If the engine will not start or stalls after start, refer to Chart A-3 in Section 6E-A of the appropriate Service Information Manual.
4. Connect a test light to 12V and probe pin "C", circuit 424 (tan/black), on the distributor side of the 4-way connector. Applying 12V to the bypass line drives the HEI module into the EST mode. With the EST line, circuit 423 (white), open the engine should quit. If the engine quits, bypass circuit operation of the HEI module is verified.
NOTE: Battery and cranking motor must be operating correctly to reach proper rpm.
5. On the distributor side of the 4-way connector jumper the EST line, circuit 423 (white) to distributor reference, circuit 430 (purple/white) . With the test light still applying voltage to the bypass line circuit 424, start the engine. Engine operation verifies that the EST circuit in the HEI module is operating normally.
6. Remove the test light while the engine is running. If the engine quits, EST grounding in the HEI module is verified. When voltage is removed from the bypass line, the module grounds the EST circuit internally. Since the EST line was jumpered to the distributor reference signal, the reference signal will be grounded causing e engine to quit.
7. If any of the above tests fail, inspect the distributor wiring for shorts or opens. If O.K., replace the ignition module.
8. Remove all jumper leads and reconnect the distributor 4-way connector.
9. Enter diagnostics and clear code 23.

Bulletin No. T 87-74
File in Group 6A
Number 88
Corp. Ref. No. 716109

Figure 1 - Revised Distributor Gear

Serviceman Bulletin T-86-79 outlines service procedures for vehicles equipped with HT4100 engines which experience abnormal distributor drive gear wear. Those procedures remain valid except that a revised distributor drive gear has recently been released. All 1987 Allantes and other 1987 vehicles beginning with the following vehicle identification numbers: (C-292647, E- 609515, K-811004) incorporate the revised gear. For service use, the revised gear is available by ordering P/N 10499813. This new part replaces P/N 10499163 for all applications. The new gear which is constructed from an improved material can be identified by two grooves above and below the roll pin as shown in Figure 1.
Warranty Considerations

Previous bulletins on this subject, such as T-86-79, have described detailed procedures for diagnosis and repair. Most important among these procedures is the requirement that when distributor driven gear wear is discovered, the distributor drive gear (camshaft) must also be replaced. The reason for this is that the two gears wear together in a pattern and when only one of the pair is replaced the likelihood of a repeat failure is very high.

In spite of this requirement, Cadillac continues to receive warranty claims indicating that only the distributor driven gear was replaced. In the interest of customer satisfaction, Labor Operation J4520-B (Distributor Driven Gear Replacement) has been cancelled. Operation T6135 described in Bulletin T-86-79 must be used for this repair.




Symptom Related Diagnostic Procedures
Fig. 3a HEI-EST ignition system diagnostic chart (Part 1 of 10). All models with remote coil
Fig. 3b HEI-EST ignition system diagnostic chart (Part 2 of 10). All models with integral coil


Wicked Wrench, ASE/GM Master Certified 25Years
Category: Cadillac
Satisfied Customers: 460
Experience: 8 time Cadillac Gold Level Excellence Award Winner
Wicked Wrench and 2 other Cadillac Specialists are ready to help you
Customer: replied 7 years ago.
I tried to test the moddule and found that the insulation for the wiring that connected to the module were cracked. I taped up the wiring and put it back. I took out the module and took it to the local parts store to have it tested but they did not have a tester. I bought a module and put it in. The car still didn't start. Looking through my different repair manuals (Chilton, Haynes) I found a test for the ingintion coil. I hooked up my meter and the coil was bad. I changed it and it started right up. Since you put me on the right path I will accept your advice.
Very Cool. Glad it worked out for you!
Wicked Wrench, ASE/GM Master Certified 25Years
Category: Cadillac
Satisfied Customers: 460
Experience: 8 time Cadillac Gold Level Excellence Award Winner
Wicked Wrench and 2 other Cadillac Specialists are ready to help you